RE: [Objectbridge-developers] OJB Homepage, OQL

[David F. <dw...@la...>]

At 09:13 AM 1/23/2001 -0500, Dixon-Peugh, David wrote:
>Except of course, that QBE by itself (without extensions),
>is capable of everything that SQL does.  (They are both
>languages for Relational Algebra after all.)

I agree that QBE is very powerful, but how does one do the equivalent of=20
"LIKE" with QBE without extensions?
Or the concept of OR's?  I'm quite interested in this.

Dave


>On another topic. . .
>
>I'm thinking about finishing up the Transaction support soon,
>however I've got some questions about how we want to implement
>it.  Perhaps you two could shed some light on what we should do.
>
>Basically, the issue is that if you use the raw JDBC driver, you
>cannot guarantee that two different connections will either both
>commit, or both abort.
>
>There are three ways around this that I can see:
>         1.  Ignore it.
>         2.  Force all JDBC connections to be the type that can
>                 participate in a distributed transaction.
>         3.  Have OJB maintain its own Transaction log which can
>                 be used to issue compensating transactions, or complete
>                 transactions when starting up again.
>
>One is the easiest to do, but you don't have real transactional integrity
>accross the database.
>
>Two will work, and it wouldn't be too hard to implement, but it limits
>which JDBC drivers can be used.  (I don't think Postgres or some of
>the other free databases have a distributed capable JDBC driver.)
>
>Three will also work, but it is obviously more work, and also leaves open
>issues about ObJectBridge interacting with other more traditional software.
>(The redo/undo of the log could overwrite something from the other App, as
>we don't have exclusive control over it.)
>
>Any suggestions?
>
>Thanks,
>
>The other David.
>
>-----Original Message-----
>From: obj...@li...
>[mailto:obj...@li...]On Behalf Of
>Mahler Thomas
>Sent: Tuesday, January 23, 2001 3:12 AM
>To: David W. Forslund
>Cc: objectbridge
>Subject: RE: [Objectbridge-developers] OJB Homepage, OQL
>
>
>
>
> > -----Urspr=FCngliche Nachricht-----
> > Von: obj...@li...
> > [mailto:obj...@li...]Im Auftrag
> > von David W Forslund
> > Gesendet: Montag, 22. Januar 2001 20:41
> > An: Thomas Mahler
> > Cc: objectbridge
> > Betreff: Re: [Objectbridge-developers] OJB Homepage, OQL
> >
> >
> > QBE, however, does not deal very well with query filters (like
> > inequality, similarity).  There should be explicit support for that
> > (which would map directly to an OQL statement).
> >
> > Dave
>
>You are right of course. I was a bit lazy with my definition of QBE. In=
 fact
>I am thinking of an "QBE with extensions" that allows composition of=
 queries
>and query filters as in the SODA approach
>(http://www.egroups.com/files/oodb/query.html) or in the approach mentioned
>in the COBRA whitepaper.
>
>
> >
> > Thomas Mahler writes:
> >  > Thanks for all your comments regarding OQL and Query by Example (QBE)
> >  > facilities.
> >  >
> >  > IMHO it's the best solution to start with a QBE-facility and only=
 after
> >  > that provide an OQL API.
> >  > Starting with QBE has 2 advantages:
> >  > - It will provide a useful extension to the PersistenceBroker, so=
 that
> >  > it can be used even without the ODMG server
> >  > - there are some working examples from other projects, that can be
> >  > easily adopted to our needs
> >  >
> >  > Implementing OQL on top of such a facility will work licke follows:
> >  > - implement a parser that reads OQL-queries and generates query=
 trees.
> >  > - provide a mapping from the abstract query trees to QBE query=
 objects.
> >  >
> >  > alternatively one could try to build a parser that directly generates
> >  > QBE query objects.
> >  >
> >  > I will have a look at all the projects you mentioned to find the best
> >  > possible start for the QBE facility. I liked the SODA approach
> >  > (www.db4o.com), but I think they are not finished with their spec.
> >  >
> >  > I'll start with this asap. Right now I'm doing some performance=
 tuning
> >  > deep inside the PersistenceBroker. I'm profiling OJB excution with=
 the
> >  > java -Xrunhprof option which gives me some hints about execution hot
> >  > spots. I already identified some hot spots in the metadata layer...
> >  >
> >  > regards,
> >  >
> >  > Thomas
> >  >
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> >  > Obj...@li...
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> >
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David W. Forslund                               dw...@la...
Computer and Computational Sciences             http://www.acl.lanl.gov/~dwf
Los Alamos National Laboratory          Los Alamos, NM 87545
505-665-1907                                    FAX: 505-665-4939